Reflex light reflector sheets (hereinafter sometimes referred to as "reflector sheets") are available on the market which have the property of directing a brilliant cone of light back towards the source of an impinging incident beam of light with relatively insignificant dispersion or diversion of about 2.degree. - 5.degree.. Such reflector sheets comprise customarily a single layer or stratum of highly refracting spherical glass beads which act as lenses and are usually referred to as high index reflex beads. These beads are either covered with a protecting layer or lacquer or the like or remain uncovered, thus to be exposed directly to the ambient atmosphere and the light. If the beads are uncovered, the reflector sheets are usually referred to as regular reflector sheets while the covered or protected bead structures are generally termed flat top reflector sheets.
Regular reflector sheets are produced with high index reflex beads of an index of refraction of about 1.9. The rear hemispheres of the beads are either coated with a mirror layer or they are mounted in a cushion layer which contains metallic flake pigment.
For the production of flat top reflector sheets, high index reflex beads of an index of refraction of &gt; 2.1 are used, the index of refraction normally eing about 2.3. If it would be feasible, from a practical point of veiw, to produce high index reflex beads of an index of refraction of 2.9, the mirror layer of flat top reflector sheets could be directly applied to the rear hemispheres of the beads, as is done in respect of regular reflector sheets. However, since with the present state of art, it is not possible to produce beads of such a high index of refraction, optical considerations require the provision of a spaced layer of predetermined thickness which is placed concentrically around the rear hemispheres of the beads, the mirror layer then being applied onto the rear face of the spacer layer (see U.S. Pat. 3,702,213). The production of such reflector sheets is extremely difficult and also, due to the multilayer construction of the sheets, very expensive. The reflection values, which are obtained with prior art reflector sheets, are far below those which are obtained with reflector products that are constructed according to the triple prism system. Further, cat's-eye reflectors of glass exceed the reflection values of prior art reflector sheets.
These are, essentially, two reasons for the poor reflection values which are obtained with prior art reflector sheets. The first reason resides in the incomplete covering of the respective area with beads, which is due to the fact that the beads are applied to the substrate either electrostatically or by mere pouring. The other reason is the spherical aberration inherent in the optics of spheres, which leads to an undesired dispersion or scattering. In respect of flat-top reflector sheets, an additional factor to be considered is the variation of the distance betwen beads and mirror layer, as well as the variations in the diameter of the high index reflex beads employed.
Additional difficulties are encountered in the production of colored reflector sheets. Thus, for example, it is known that regular reflector sheets, which have a rear mirror layer, cannot be produced in colored form at all. As regards flat-top reflector sheets, it is difficult to obtain a color impression or appearance which is the same during nighttime and daytime light conditions.